The present invention relates to an optically active benzothiepin derivative possessing osteogenesis-promoting activity, bone resorption-suppressing activity and other activities, and a bone disease prophylactic or therapeutic agent comprising it as an active ingredient.
Bone disease is a pathologic state or disease involving some symptom or risk due to quantitative reduction in bone exceeding a specified amount. Major symptoms of osteoporosis, a bone disease, are for example, spinal kyphosis, and fractures of dorsolumbar bones, vertebral centra, femoral necks, lower end of radius, ribs, and upper end of humerus. In healthy bone tissue, bone destruction occurs continuously, with a good balance between bone formation and resorption. Osteoblasts and osteoclasts, respectively, play key roles in bone formation and resorption. Deterioration of the balance therebetween results in quantitative reduction in bone. Traditionally, bone resorption suppressors, such as estrogens, calcitonin and bisphos-phonates, have been primarily used to prevent and treat osteoporosis. However, these bone resorption suppressors fail to achieve satisfactory effect in some cases, due to limitations of the subject or to uncertain efficacy.
Alternatively, the present inventors have discovered a sulfur-containing heterocyclic compound possessing excellent bone resorption-suppressing activity, a compound represented by the following general formula (A) or (B), or a salt thereof (Japanese Pat. Unexamined Publication Nos. 232880/1991 and 364179/1992). 
wherein ring A is a benzene ring that may be substituted; R represents a hydrogen atom or a hydrocarbon group that may be substituted; B represents a carboxyl group that may be esterified or amidated; X represents xe2x80x94C H(OH)xe2x80x94 or xe2x80x94COxe2x80x94, k represents 0 or 1, kxe2x80x2 and n each represent 0, 1 or 2.
An example of such a compound is a compound represented by formula (C): 
has been described.
There is a need for the development of a prophylactic or therapeutic agent having improved properties (stability, absorbability, bioavailability etc.) for clinically useful pharmaceuticals (especially oral preparations).
The present inventors conducted intensive investigation to develop a clinically more useful drug that has direct action on the bone, suppresses bone resorption, and promotes bone formation, and for the first time synthesized an optically active benzothiepin derivative represented by formula (I): 
wherein R represents a lower alkyl group; R1 and R2 independently represent a lower alkyl group, or may bind together to form a ring; and found that this compound is unexpectedly very useful clinically among the compounds represented by formula (A) or (B) above, and is particularly effective in osteogenesis-promoting activity and oral absorbability etc. For example, the optically active benzothiepin derivative of the formula (I) is superior to the compound of the formula (C) in oral absorbability. The present inventors conducted further investigation based on this finding, and developed the present invention.
Accordingly, the present invention relates to:
(1) An optically active compound of the formula (I): 
wherein R represents a lower alkyl group; R1 and R2 independently represent a lower alkyl group, or together represent a lower alkylene,
(2) A compound according to the above (1), wherein R, R1 and R2 independently are a C1-4 alkyl group,
(3) A compound according to the above (1), which is (2R,4S)-(xe2x88x92)-N-[4-(diethoxyphosphorylmethyl)phenyl]-1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxamide,
(4) A method of producing an optically active compound of the formula (I): 
wherein R represents a lower alkyl group; R1 and R2 independently represent a lower alkyl group, or may bind together to form a ring, by reacting an optically active compound of the formula (II): 
wherein R is defined as noted above, or its derivative reactive or salt at the carboxyl group, with a compound of the formula (III): 
wherein R1 and R2 are defined as noted above, or its derivative reactive or salt at the amino group,
(5) An optically active compound of the formula (II): 
wherein R represents a lower alkyl group, or its derivative reactive or salt at the carboxyl group,
(6) An osteogenesis promoter comprising an optically active compound of the formula (I) according to the above (1),
(7) An osteogenesis promoter according to the above (6), which is orally absorbable,
(8) A prophylactic or therapeutic agent for bone diseases comprising an optically active compound of the formula (I) according to the above (1),
(9) A promoter for cure of bone fracture comprising an optically active compound of the formula (I) according to the above (1),
(10) A method of promoting osteogenesis in a mammal which comprises administering to said mammal in need an effective amount of an optically active compound of the formula (I) according to the above (1),
(11) A method of preventing or treating bone diseases in a mammal which comprises administering to said mammal in need an effective amount of an optically active compound of the formula (I) according to the above (1),
(12) A method of promoting cure of bone fracture in a mammal which comprises administering to said mammal in need an effective amount of an optically active compound of the formula (I) according to the above (1),
(13) Use of an optically active compound of the formula (I) according to the above (1) for the manufacture of an osteogenesis promoter,
(14) Use of an optically active compound of the formula (I) according to the above (1) for the manufacture of a prophylactic or therapeutic agent for bone diseases, and
(15) Use of an optically active compound of the formula (I) according to the above (1) for the manufacture of a promoter for cure of bone fracture.
With respect to the above formulas, the lower alkyl group represented by R, R1 or R2 is exemplified by straight chain or branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl and hexyl. R1 and R2 may represent together a lower alkylene, in which case 
may represent 
(n represents an integer from 2 to 4).
Preferably, R, R1 and R2 are each an alkyl group having 1 to 4 carbon atoms, such as methyl or ethyl.
The compound (I) of the present invention, an optically active compound of the (2R,4S) configuration, preferably contains substantially no compounds of the (2S,4R) configuration, and has an optical purity of nearly 100%.
Of the compounds of formula (I), (2R,4S)-(xe2x88x92)-N-[4-(diethoxyphosphorylmethyl)phenyl]-1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxamide etc. are preferred.
Compound (I) is produced by reacting an optically active compound represented by formula (II), or its derivative reactive or salt at the carboxyl group, with a compound represented by formula (III), or its derivative reactive or salt at the amino group.
Preferable derivatives of compound (III) reactive at the amino group thereof include Schiff""s base type imino or enamine form tautomeric isomers resulting from reaction of compound (III) and a carbonyl compound such as aldehyde (e.g., acetaldehyde) or ketone (e.g., acetone); silyl derivatives resulting from reaction of compound (III) and a silyl compound such as bis(trimethylsilyl)acetamide, mono(trimethylsilyl)acetamide or bis(trimethylsilyl)urea; and derivatives resulting from reaction of compound (III) and phosphorus trichloride or phosgene.
Preferable derivatives of compound (II) reactive at the carboxyl group thereof include acid halides, acid anhydrides, activated amides and activated esters, all obtained by conventional methods. More specifically, such preferable reactive derivatives include acid chlorides; acid azides; mixed acid anhydrides such as those with a substitutional phosphoric acid such as dialkylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, dibenzylphosphoric acid or halogenated phosphoric acid, or with dialkylphosphorous acid, sulfurous acid, thiosulfuric acid or sulfuric acid, or with a sulfonic acid such as methanesulfonic acid, or with an aliphatic carboxylic acid, such as acetic acid, propionic acid, butyric acid, isobutyric acid, pivalic acid, pentanoic acid, isopentanoic acid or trichloroacetic acid, or with an aromatic carboxylic acid such as benzoic acid; symmetric acid anhydrides; activated amides with imidazole, 4-substitutional imidazole, dimethylpyrazole, triazole or tetrazole; activated esters such as cyanomethyl ester, methoxymethyl ester, dimethyliminomethyl ester, vinyl ester, propargyl ester, p-nitrophenyl ester, tri-chlorophenyl ester, pentachlorophenyl ester, mesylphenyl ester, phenylazophenyl ester, phenylthio ester, p-nitrophenyl ester, p-cresylthio ester, carboxymethylthio ester, pyranyl ester, pyridyl ester, piperidyl ester and 8-quinolylthio ester; and esters with N-hydroxy compounds such as N,N-dimethylhydroxylamine, 1-hydroxy-2-(1H)-pyridone, N-hydroxysuccinimide, N-hydroxyphthalimide, 1-hydroxy-1H-benzotriazole and N-hydroxy-5-norbornane-2,3-dicarboximide. These reactive derivatives can be optionally chosen according to the type of compound (II) used.
Preferable salts of reactive derivatives of compound (II) or (III) include salts with bases, exemplified by alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, ammonium salt, and organic base salts such as trimethylamine salt, triethylamine salt, pyridine salt, picoline salt, dicyclohexylamine salt and N,N-dibenzylethylenediamine salt.
This reaction is normally carried out in a commonly used solvent such as water, an alcohol such as methanol or ethanol, acetone, dioxane, acetonitrile, chloroform, methylene chloride, ethylene chloride, tetrahydrofuran, ethyl acetate, N,N-dimethylformamide or pyridine, but can be carried out in any other organic solvent, as long as it does not interfere with the reaction. These ordinary solvents may be used in mixture with water. When compound (II) or (III) is used in the form of free acid or salt thereof, this reaction is preferably carried out in the presence of an ordinary condensing agent, e.g., N,Nxe2x80x2-dicyclohexylcarbodiimide; N-cyclohexyl-Nxe2x80x2-morpholinoethylcarbodiimide; N-cyclohexyl-Nxe2x80x2-(4-diethylaminocyclohexyl)carbodiimide; N,Nxe2x80x2-diethyl-carbodiimide; N,Nxe2x80x2-diisopropylcarbodiimide; N-ethyl-Nxe2x80x2-(3-dimethylaminopropyl)carbodiimide; N,Nxe2x80x2-carbonylbis(2-methylimidazole); pentamethyleneketene-N-cyclohexylimine; diphenylketene-N-cyclohexylimine; ethoxyacetylene; 1-alkoxy-1 -chloroethylene; trialkyl phosphite; ethyl polyphosphate; isopropyl polyphosphate; phosphorus oxychloride; diphenylphosphorylazide; thionyl chloride; oxalyl chloride; a lower alkyl haloformate such as ethyl chloroformate or isopropyl chloroformate; triphenylphosphine; 2-ethyl-7-hydroxybenzisoxazolium salt, 2-ethyl-5-(m-sulfophenyl)isoxazolium hydroxide intramolecular salt; N-hydroxybenzotriazole; 1-(p-chlorobenzenesulfonyloxy)-6-chloro-1H-benzotriazole; or in what is called Vilsmeier""s reagent (as prepared by reaction of N,Nxe2x80x2-dimethylformamide with thionyl chloride), phosgene, trichloromethyl chloroformate, phosphorus oxychloride, or the like. It is also preferable to use a condensing agent such as N,Nxe2x80x2-dicyclohexylcarbodiimide in the presence of N-hydroxybenzotriazole or N-hydroxy-5-norbornan-endo-2,3-dicarboximide. This reaction may also be carried out in the presence of an inorganic or organic base such as alkali metal hydrogen carbonate tri(lower)alkylamine, pyridine, N-(lower)-alkylmorpholine or N,N-di(lower)alkylbenzylamine. Although the reaction temperature is not subject to limitation, this reaction is normally carried out under cooling to heating (xe2x88x9210 to 120xc2x0 C.) conditions. Reaction time is normally about 0.5 to 100 hours, preferably about 1 to 50 hours.
Compound (I) thus obtained may be isolated and purified by known means of separation and purification such as concentration, concentration under reduced pressure, solvent extraction, crystallization, recrystallization, redissolution and chromatography.
Starting compound (II) can, for example, be produced by optically resolving the racemate of compound (II) disclosed in Japanese Pat. Unexamined Publication No. 364179/1992. Specifically, an optically active compound is produced by preparing a salt of the racemate of compound (II) and an optically active base (e.g., optically active a-methylbenzylamine, brucine, quinine, cinchonine), repeating fractional crystallization based on the solubility difference between the resulting diastereomers to obtain a sparingly soluble salt in pure form, then performing acid treatment. As another method, the optically active compound can be produced by esterifying the racemate of compound (II) with an optically active alcohol (e.g., optically active methyl lactate, methyl mandelate), preparing one of the resulting diastereomers of the ester in pure form on the basis of the physical property difference between the diastereomers, and then performing hydrolysis.
Compound (I), the desired compound of the present invention, can be prepared as solid preparations such as tablets, capsules, granules and powders, or liquid preparations such as syrups and injectable preparations, as formulated with pharmaceutically acceptable carriers, by conventional methods, and can be administered orally or non-orally. The content ratio of compound (I) is normally about 0.01 to 95% by weight, preferably about 0.1 to 20% by weight, relative to the entire preparation. Compound (I) is preferably used as an oral preparation.
Pharmaceutically acceptable carriers are various organic or inorganic carrier substances in common use as pharmaceutical materials, including excipients, lubricants, binders and disintegrating agents for solid preparations, and solvents, dissolution aids, suspending agents, isotonizing agents, buffers and soothing agents for liquid preparations. Other pharmaceutical additives such as preservatives, antioxidants, coloring agents and sweetening agents may be used as required. Preferable excipients include lactose, sucrose, D-mannitol, starch, crystalline cellulose and light silicic anhydride. Preferable lubricants include magnesium stearate, calcium stearate, talc and colloidal silica. Preferable binders include crystalline cellulose, sucrose, D-mannitol, dextrin, hydroxypropyl cellulose, hydroxypropylmethyl cellulose and polyvinylpyrrolidone. Preferable disintegrating agents include starch, carboxymethyl cellulose, carboxymethyl cellulose calcium, crosscarmelose sodium and carboxymethyl starch sodium. Preferable solvents include water for injection, alcohol, propylene glycol, macrogol, sesame oil and corn oil. Preferable dissolution aids include polyethylene glycol, propylene glycol, D-mannitol, benzyl benzoate, ethanol, tris-aminomethane, cholesterol, triethanolamine, sodium carbonate and sodium citrate. Preferable suspending agents include surfactants such as stearyltriethanolamine, sodium lauryl sulfate, laurylaminopropionic acid, lecithin, benzalkonium chloride, benzethonium chloride and monostearic glycerol; and hydrophilic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose sodium, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose. Preferable isotonizing agents include sodium chloride, glycerol and D-mannitol. Preferable buffers include buffer solutions of phosphates, acetates, carbonates and citrates. Preferable soothing agents include benzyl alcohol. Preferable preservatives include p-oxybenzoic acid esters, chlorobutanol, benzyl alcohol, phenethyl alcohol, dehydroacetic acid and sorbic acid. Preferable antioxidants include sulfites and ascorbic acid.
Since the compound represented by general formula (I) possesses potent bone resorption-suppressing activity and osteogenesis-promoting activity, and is more excellent in properties related to clinical utility, such as stability, absorbability and bioavailability, it is useful as an osteogenesis promoter and it can be used to prevent or treat various bone diseases, such as osteoporosis and bone fracture, in mammals (e.g., humans, rats, mice, cats, dogs, rabbits, bovines, swines). The compound (I) of the present invention can be safely used with low toxicity. For example, when compound (I) was orally administered to rats at a dose of 500 mg/kg/day for 2 weeks, no abnormal findings were obtained. The compound (I) is especially superior to the corresponding racemic compound in absorbability when orally administered, and is therefore useful for an orally administrable preparation.
More specifically, the optically active benzothiepin derivative relating to the present invention, represented by general formula (I), possesses excellent alkaline phosphatase induction activity, hence showing excellent osteogenesis-promoting action, and is useful as a drug for preventing or treating metabolic bone diseases, including osteoporosis. Any osteogenesis promoter comprising the compound (I) of such activity of the present invention is applicable to the treatment of bone fractures, bone defects, and bone diseases such as osteoarthritis in the field of orthopedics and periodontal diseases. Such a promoter is also expected to be effective in the field of dentistry, for repair of periodontal tissue defects due to periodontitis, stabilization of artificial tooth roots, ridge formation and repair of cleft palate etc.
When used as a prophylactic or therapeutic agent for osteoporosis, for instance, the compound represented by general formula (I) is administered at a daily dose of 5 to 1,000 mg, preferably 30 to 600 mg, as active ingredient (I), depending on patient condition and weight and method of administration, in the case of oral administration for each adult (weighing 50 kg), in 1 to 3 portions per day.
The compound (I) of the present invention can be used in combination with other bone resorption-suppresors and osteogenesis promoters such as Vitamin Ds (ex. 1xcex1-hydroxyvitamin D3, 1xcex1, 25-dihydroxyVitamin D3, Flocalcitriol, Secalciferol, etc.), Calcitonins (ex. Calcitonin eel, Calcitonin salmon, Calcitonin porcine, Avicatonin, etc.), Bisphosphonic acid derivatives (ex. Etidronate, Cimadronate, Alendronate, Tiludronate, Risedronate, Clodronate, YH-529, etc.), Sex hormone related compounds (ex. Tibolone, Estradiol, Osaterone, Raloxifene, Droloxifene, Ormeloxifene, Tamoxifen, Mifepristone, etc.), Ipriflavone, Vitamin K2 (ex. Menatetrenone), Sodium fluoride and PTH derivatives (ex. PTH(1-34), PTH(1-84), PTH(1-36), etc.)